Load/Store Synchronization for Selective Hazard Ordering
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Solution Overview
Problem
Existing data processing systems face challenges in efficiently controlling the ordering of load/store operations, particularly in enforcing that younger operations observe the results of older operations within overlapping address ranges, which can be complex and costly to implement.
Innovation Solution
Implementing load/store processing circuitry with a predetermined-class store buffer and an instruction decoder to enforce result observation for specific classes of load/store operations, allowing store-to-load forwarding only within the class and simplifying hardware logic by using dedicated buffers and pipelines for less frequent synchronization needs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If hardware circuit logic is used to manage ordering enforcement for all load/store operations, then ordering correctness is ensured, but device complexity and implementation cost increase
Solution Approach 1:
The patent segments load/store operations into two distinct classes: predetermined-class operations (e.g., stack operations) and non-predetermined-class operations. Separate store buffers are maintained for each class, allowing simplified hazard checking logic that only needs to enforce ordering within the predetermined class, rather than for all operations. This segmentation reduces the complexity of hardware circuit logic while maintaining ordering correctness for the critical predetermined class.
Solution Approach 2:
The patent applies different levels of ordering enforcement to different classes of operations. For predetermined-class operations, strict ordering enforcement is implemented using dedicated store buffers and synchronization instructions. For non-predetermined-class operations, relaxed ordering is permitted. This local differentiation allows the system to maintain reliability where needed while reducing overall device complexity.
2Productivity
If store-to-load forwarding is implemented for all operations, then performance is improved, but device complexity increases due to comprehensive hazard checking requirements
Solution Approach 1:
The patent segments the store buffer into separate buffers for predetermined-class and non-predetermined-class operations. Store-to-load forwarding is implemented only within the predetermined class, where it provides performance benefits. The hazard checking logic is simplified because it only needs to manage forwarding for operations within the same class, rather than handling all possible operation combinations.
Solution Approach 2:
The patent implements store-to-load forwarding partially, only for predetermined-class operations, rather than for all operations. This partial implementation achieves performance improvement for the critical path (stack operations) while avoiding the complexity of comprehensive hazard checking for all operation types.
3Reliability
If comprehensive hazard checking is performed for all load/store operations, then ordering correctness is ensured, but power consumption increases
Solution Approach 1:
By segmenting operations into predetermined and non-predetermined classes with separate store buffers, the patent enables selective hazard checking. The system performs comprehensive hazard checking only for predetermined-class operations where ordering correctness is critical, while using relaxed checking for non-predetermined operations. This segmentation significantly reduces the total power consumption of hazard checking circuitry.
Solution Approach 2:
The patent applies different levels of hazard checking to different operation classes. Strict hazard checking is localized to predetermined-class operations, while relaxed checking is applied to non-predetermined operations. This local quality differentiation reduces overall power consumption while maintaining reliability where it matters most.
Data Source
AI summary
For a predetermined class of load/store operations, load/store processing circuitry buffers store data of predetermined-class store operations in a predetermined-class store buffer, and controls store-to-load forwarding of store data from that buffer to predetermined-class load operations. A predetermined-class-load/store synchronization instruction controls the load/store processing circuitry to enforce that, for a hazarding younger non-predetermined-class load/store operation occurring after the predetermined-class-load/store synchronization instruction in program order and a hazarding older predetermined-class store operation occurring before the predetermined-class-load/store synchronization instruction in program order, for which address ranges overlap, the hazarding younger non-predetermined-class load/store operation observes a result of the hazarding older predetermined-class store operation. In absence of any intervening predetermined-class-load/store synchronization instruction between a given older predetermined-class store operation and a given younger non-predetermined-class load/store operation with overlapping address range, the given younger non-predetermined-class load/store operation is permitted to fail to observe a result of the given older predetermined-class store operation.